Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$172.60	10.239%	$190.2725	$190.27	$190.25	$190.30
Purchase #2	$38.99	12.457%	$43.847	$43.85	$43.85	$43.80
Purchase #3	$246.92	12.119%	$276.8442	$276.84	$276.85	$276.80
Purchase #4	$204.92	13.852%	$233.3055	$233.31	$233.30	$233.30
Purchase #5	$82.88	6.681%	$88.4172	$88.42	$88.40	$88.40
Purchase #6	$57.50	7.507%	$61.8165	$61.82	$61.80	$61.80
Purchase #7	$41.86	11.857%	$46.8233	$46.82	$46.80	$46.80
7 purchase totals =	$845.67		$941.3262	$941.33	$941.25	$941.20